Surface protection for magnesium alloys



"Patented June 17, 1930 UNITED s'm'rss PATENT OFFICE nussELI'. n. LOWE, on NEW YORK, N. y nssrenoa T0 DOHEB'I'Y nnsmncn COMPANY, or NEW YORK, N. Y., A CORPORATION OFDELAWARE V SURFACE PROTECTION FOR MAGNESIUM ALLOYS No Drawing.

however, exhibit a tendency to surface corro-.

sion in the presence of hot water even if the water iscomparatively free from traces of corroding chemicals. This tendency to corrosion has seriously mitigated against the use of magnesium alloys in laces where they would otherwise be particu arly desirable on account of their lightness and great strength.

This invention has-among its objects to modify the surface of magnesium alloys in such a manner that the surface shall be able to withstand the corroding effects of various corroding fluids but more particularly hot water.

tion, the preferred process being as follows: The surface of the magnesium-alloy object or Another object is to provide a simple and easily practiced process for treating the surface of magnesium alloys to effect such surface change as will enable them to withstand the corroding effects of hot water.

In accordance with the present invention, I providemagnesium alloys with a surface coating of a phosphorus compound. This coating preferably consists of a surface film of ammonium-magnesium-phosph'ate. Magnesium phosphate alone forms a coating which very materially resists the corroding action of hot water and in many applications of the metal will prove suflicient for its intended purpose.

ferred.

The manner of applying the protective coating is an important feature of the inven- The combination of the two salts, however, provides a more resistant surface and is consequently to be pre- Application filed mm. 14, 1927. Serial No. 175,429.

in a relatively weak solution of phosphoric acid, a 5% solution being preferred, and is allowed to remain in the solution until a black 7 film has developed after which it is removed from-the solution and washed. The coating thus provided greatly improves the hotwater-corrosion-resisting qualities of the alloy object and the object thus treated may be used without further surface treatment. A more resistant coating is, however, very desirable in many applications of the metal. I prefer, therefore, to continue further surface treatment as follows: After the first coating has been applied as specified, I immerse'the object in a relatively weak solution of ammonium phosphate, preferably a 5% solution. The time of immersion should be rather extended. The best results are indi cated when the time of immersion is from 2 to 5 days, the time varying to some extent with the strength of the solution. After heing removed from the solution the object is washed and flame dried and is then ready for use. The practical limits of both the phosphoric acid solution and ammonium phosphate solution have been found to be'between 4% to 6%.

What I claim is: I

1. A magnesium alloy provided with a surface coating of a double salt of phosphoric acid.

2. A magnesiumalloy provided with a surfzlrlce coating of ammonium magnesium phosp ate. T

3. A method of providing magnesium alloy with a protective coating comprising initially immersing said alloy in a 4% to 6% solution of phosphoric acid long enough to allow a film to form thereon, and finally immersingit in a 4% to 6% solution of ammo nium phosphate for a period ranging between two to five days, washing, and heat drying the coating thus formed.

4. A method of providing magnesium alloy with a protective coating comprising initially dipping said alloy in a mild cleaning solution of nitric acid, washing, immersing said alloy in a 5% solution of phosphoric 7-5 itlally dipp' Solution ofommonimn phosphate for aperiod v of twoto five'days, v 3 5. A method of providing magnesium al- 10y with a. protective coating comprising insaida11oyinai18%to12% cleamng solution ofnitric a'cid, washing, immersing said alloy in a 4% to 6% solutlon of phosphoric acid long enough to allow a. phosphate film to form, and finally A it in-a. 4% to 6% solution of ammonium phosphate for a period. of more than twenty-0111- houi's. In testimony whereof I aflix my si ature.

RUSSELL E; L WE. 

